<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div {
            height: 100px;
            width: 100px;
            background: red;
            transition: width 1s ease;
        }
        div:hover {
            width: 200px;
        }
    </style>
</head>
<body>
    <div></div>

    <script>

        const div = document.querySelector('div');

        let angle = 0;

        // 帧函数
        function frame () {
            // console.log(3);
            div.setAttribute('style', `transform: rotate(${ angle }deg)`);
            angle++;
            // 执行下一帧
            requestAnimationFrame(frame); // 3
        }

        console.log(1);
        // 专门做动画的
        // js做动画的唯一途径
        // 执行一帧
        requestAnimationFrame(frame); // 3

        console.log(2);

    </script>
</body>
</html>